The invention generally relates to the non-destructive analysis of industrial products and more particularly to using dual energy x-ray attenuation measurements to determine the composition of products in an industrial environment.
In industry it is often important to determine the composition of the product for purposes of quality control. Similarly, particularly in the food industry, it is important to locate contaminants or identify certain substances the quantity of which must be controlled. Moreover, it is desired to test the product without destroying it or altering its make-up in any way.
As one example, it is often important to determine the fat and bone content of cut or processed meat, since the price of meat is based largely on the amount of lean meat being sold. Also, processed meat may contain bone fragments or other objects from the sawing and boning process that could injure a consumer or otherwise substantially reduce the value of the meat.
Techniques of chemical analysis of industrial products, such as for determining the amount of fat in meat, are well known, but such laboratory techniques are time consuming and costly. Moreover, these techniques typically require that the product be physically or chemically broken down, consequently, only selected samples of the product can be analyzed, rather than each product. This diminishes the accuracy of the analysis since the quantities of substances and contaminants can vary from one product to another.
One non-destructive method of analyzing products uses x-ray or gamma radiation. For example, U.S. Pat. Nos. 2,992,332 and 4,168,431 describe systems detecting attenuation of x-rays passing through the product. Using such methods, each product rather than just samples, can be analyzed. Unfortunately, accurate x-ray attenuation determinations of compositions of matter require all other variable, particularly the density and total thickness of the sample to be precisely controlled.
U.S. Pat. No. 4,504,963 suggests that the need for careful product sample preparation (to ensure constant density and thickness) can avoided by using at least three separate x-ray beams, each operating at a different energy level. According to the application, the multiple x-ray beams each provide a different attenuation value and thus provide a xe2x80x9csignaturexe2x80x9d that may be empirically related to a particular composition, regardless of slight density or thickness variations in the product. This approach, if feasible, thus avoids the problems inherent in preparing uniform product samples for testing. Nevertheless, it requires both multiple measurements of the product at various densities and thicknesses so as to deduce the signature ranges. Further, there is no indication that a unique signature will be available for products other than meat.
There is a need for a simple method for rapidly determining the composition of products without the need for careful sample preparation and that works over a range of different products.
The present inventors have recognized that dual energy x-ray analyses, developed originally for medical imaging, can be used to make industrial composition measurements of irregular samples. The dual energy technique provides an indication of relative proportions of different materials that make up a composition largely indifferent to total material mass or density of the composition. Thus careful preparation of the samples is not required. Further, the theoretical basis of this imaging technique allows any two materials exhibiting different electron densities and atomic numbers to be distinguished.
Specifically then, the present invention provides a method of non-destructive analysis of binary industrial compositions including a first step of selecting a first and second basis material expected to compose the binary industrial composition. A beam of x-ray radiation having first and second energies is then generated and the binary industrial compositions are inserted into the beam such that the beam traverses an arbitrary mass of the portions varying between compositions. The attenuation of the x-ray beam after passage through the binary industrial compositions at the first and second energy is then detected and from this, a relative proportion defining a mass ratio of the selected first and second material is deduced such as would provide a photoelectric absorption and Compton scattering consistent with the attenuation of the x-rays at the first and second energy. Data is then output to a user indicating this relative proportion.
Thus it is one object of the invention to make use of a modeling of Compton scattering and photoelectric absorption to cancel out effects caused by varying thicknesses, densities, and inhomogeneities in the measured material and in this way provide a flexible industrial measuring tool applicable to a wide variety of material where extensive sample preparation is impractical.
The method may include the further step of deducing from the attenuation of the x-rays at the first and second energy, the total mass traversed by the beam. This mass may be output or used with the relative proportion to output masses of the first and second material.
Thus it is another object of the invention to provide total mass value in addition to the proportions of two basis materials in a binary industrial composition. The same modeling process that allows the measurement of proportion to be indifferent to the quantity of the material to be measured allows the quantity to be deduced. This total mass value can provide additional information useful, for example, in combining relative proportion measurements for different samples in a mass weighted average.
The x-ray beam may be operated on a continuous basis as the binary industrial compositions are moved through the beam along a path, and the path length during which the binary industrial compositions are moved through the beam may be measured to producing a total composition mass as a time integral of the total mass traversed by the beam. In this regard, a conveyor holding the binary industrial compositions may perform movement of the compositions and the conveyor may include a sensor providing a measure of path length of movement of the binary industrial compositions. The binary industrial compositions may be constrained in extent perpendicular to the beam axis and the path such that the constrained extent lies wholly within the beam.
Thus it is another object of the invention to allow quantitative assessment of a loosely aggregated binary industrial composition. By constraining the composition only to lie within the beam width without regard to height or length, the composition can be fully characterized as it passes through the beam.
Creating the x-ray beam may make use of two x-ray tubes, each providing different x-ray energy. The two x-ray tubes may be operated at different voltages and/or be filtered using different filters. Two separate x-ray detectors may be used to measure the attenuations at the two energies with each x-ray tube directing a beam to a different one of the detectors. The x-ray detectors may optionally be preferentially sensitive to a different one of the first and second x-ray energy.
Thus it is another object of the invention to greatly simplify the manufacture of a device for dual energy industrial inspections by using two x-ray tubes and possible dedicated detectors that may be optimized for their one particular energy measurement.
An image of a first basis material image based upon the proportion determined at different points through the binary industrial compositions may be developed and used for monitoring the presence of foreign bodies of the first basis material.
Thus it is another object of the invention to provide material selective images such as may be used to improve conventional machine vision techniques for the detection of foreign bodies in industrial products.
The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration preferred embodiments of the invention. Such embodiments do not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention.